1. Field of the Invention
The present invention is directed to luminaires for providing a uniform illumination on a planar surface and more specifically to the reflector for such a luminaire to achieve such uniform illumination.
2. Background of the Invention
In order to provide uniform horizontal illumination on a plane, it is a well known fact that the inverse square law E= I cos.theta./d.sup.2 must be satisfied. In order to provide constant illumination the luminaire must provide 13.245 times the intensity at angle .theta. of 65.degree. as is provided at nadir. This contribution must be the sum of both the direct and reflected components. If the direct component is the same at both nadir and 65.degree., the reflected component at 65.degree. must satisfy the following relationship:
Direct component (65.degree.)+ reflected component (65.degree.)= 13.245 (direct component 0.degree. + reflected component 0.degree.).
In determining the resultant luminaire distribution and contour it is necessary to take into consideration the size of the light source as well as its position relative to the reflector contour.
Various reflector schemes have been devised in an attempt to provide uniform illumination on the horizontal plane. Most attempts have failed because the investigators did not consider all of the factors which affect the radiation emanating from the luminaire. Some of the factors include light source size, relationship of source to the contour, optical character of the reflecting material and/or refracting material, physical blockages imposed by other components, etc.
Some prior art luminaires have utilized reflectors which are comprised of parabolic and elliptical curves in an attempt to achieve an even light distribution of a planar surface. Some of these prior art luminaires specifically avoided the use of cylindrical curvatures for any part of the reflector since it was considered undesirable to have the light reflected directly back through the light source which would be located at the center of the cylindrical portion.